Process for sweetening gasoline



Dec. 7, 1943. c. D. LowRY, JR., ET AL PROCESS FOR SWEETENING GASOLINEFiled Aug. 15, 1940 Patented Dec. 7, 1943 PROCESS Fon swEETENiNGGASOLINE Charles Doak Lowry, Jr., and Robert E. Sutherland, Chicago,Ill., assignors to Universal Oil Products Company, Chicago, ll., acorporation of Delaware Application August 15, 1940, Serial No. 352,684

(Cl. 19d-32) 2 Claims.

This invention relates to a process for treating hydrocarbon oil toimprove the odor thereof. More particularly it relates to a process forsweetening hydrocarbon distillate of gasoline boiling range.

In one specific embodiment the present invention is a process fordesulfurizing and sweetening gasoline for the purpose of improving thevaluable characteristics thereof which comprises contacting saidhydrocarbon oil with an aqueous solution of an alkali metal hydroxide,recovering the solution and regenerating it, separating the gasoline,mixing it with sodium plumbite solution, adding thereto` sufcient sulfurto bring about the sweetening reaction, further mixing the mixture,removing a major portion of the spent doctor solution, contacting thesweetened gasoline 'with an additional portion of fresh doctor solution,separating the gasoline and removing remaining treating solutiontherefrom, subjecting said spent doctor solution to reactivation in thepresence of air and returning a portion of the regenerated solution forfurther use in the process.

The process as practiced is illustrated in the accompanying drawingwhich is diagrammatic and not drawn to scale.

Sour gasoline is introduced through line valve 2, pump 3 and valve 4 toabsorber 5 which is a vertical tower wherein contact between an aqueoussolution of an alkali metal hydroxide such as sodium hydroxide,otherwise known as caustic soda, is effected at a temperature ofapproximately 50-100 F. The tower may be equipped with contactingmembers such as side-to-side baliles, perforated plates, bubble decksand the like. In starting up the process, aqueous caustic solution isintroduced through line 5, valve l, pump 8, line 9 and valve IU to thetop of absorber 5. After the process has continued to operate, makeupcaustic is introduced through this line. The caustic solution may beused in concentrations of approximately 5-50%, although a solution ofabout concentration is usually used. Spent caustic solution is withdrawnfrom the absorber through line valve I2 and heater l2', entering the topof regenerating tower I 3. Steam is introduced at the bottom of thetower through line I4 and valve I5, passing upward countercurrent to thespent caustic solution. Mercaptans are hydrolyzed by the action of thesteam under the reactivating conditions which are normally in the rangeof approximately 160- 250 F. The mercaptans are removed through line I6and valve |f`| to be disposed of. Ihe re-` generated caustic solution ispassed through line 8 and valve I9 by pump 8 to line 9 and thence toabsorber 5. The caustic-scrubbed gasoline, which by this treatment isappreciably reduced in mercaptan content, is passed through line 20 andvalve 2| to mixer 22. Sodium plumbite solution is mixed with thegasoline, entering from line 8|. Mixer 22 may be any type of mixer, suchas orifice plates or pipe mixers containing baliles and the like. Thegasoline after leaving the mixer is blended with additional gasolinecontaining elemental sulfur, entering from sulfur pot 23 through line 24and valve 25. Sufficient sulfur is added to cause a reaction between thelead mercaptides in the gasoline,V thereby converting the mercaptans toalkyl disuldes and lead sulfide. The mixture passes through mixer 26where additional mixing and reaction occurs, and from thence intosettler 2l. The treated mixture is usually introduced through a spraynozzle at a point below the surface of the gasoline in settler 21. Amajor portion of the spent doctor solution together with lead sulfide insuspension separates from the gasoline. The spent treating agent isremoved through line 28 and valve 29 yto line 30 and thence to settler3| wherein it is treated as hereinafter described. A level of doctorsolution is maintained in settler 2l at all times. Treated gasolinewhich may contain small amounts of suspended doctor solution and leadsulde is removed through line 32 and valve 33 to coagulator 34. Thecoagulator is a vertical drum containing fresh doctor solution which isintroduced through line 35 and valve 36, and a portion of which may beremoved through line 81, valve 38 to line 28 and thence to settler 3|.The gasoline is introduced at the bottom of the coagulator through aspray in order to insure adequate contact with the doctor solution atthis point. By this means any unreacted mercaptans are caused to reactand lead sullide is to a large extent coagulated into particles whichare more readily separated from the sweetened gasoline. The gasolinepasses overhead through line 39 and valve 40 to settler 4|. Here againit is introduced through a spray below the surface of the liquid. Thespent treating solution and lead sulde separates substantiallycompletely from the gasoline in this settler and is removed through line42 and valve 43 to line 38 and thence to settler 3|. The sweetenedgasoline is removed fromsettler 4| through lines 44 and 45 and valve 46to filter 41 which may comprise a drying tower, sand lter or a waterwashing tower to remove remaining traces of entrained alkalinesolution..Suchlof the solution as 44 may be passed through line 52, valve 53 and'i pump 53 to`sulfur pot 23, which -contains lumps or rolls of sulfur, apart of which dissolves in the gasoline and is used in the svveeteningreaction. y

The spent doctor solution in settlertvl may be passed through line 54,valve 55,-'pump 56 and valve i to regenerating tower 58. Steam may beadded through line 59 and valve E50, and air for eecting theregeneration may be added through line Si and valve 62. The regeneratingtower containing contacting members such as baiiies or perforated platesfor effecting adequate contact between the spent treating solution andthe column may be drained, when desired through line 53 and valve64...*Tl1e regenerated solution isrremoved through line 55 and valve 66to `.storage tank lE'. The regeneration of doctor solution is usuallycarried out ata temperature of approximately 1Y0-250 YF., and it hasbeen found that the use of slightly superatmospheric pressure, say ofthe order of 25-100 pounds per square inch on the regenerating tower 53is helpful in obtaining complete reactivation. A portion of the solutionmay be passed through line E8 and valve t5!4 to line 30 and thusrecirculated for additional regeneration. Gasoline which may becontained in the spent treating solution may be removed from settler 3|by Way of line l and valve il to the sump. The tank is further providedwith line I2 and valve: 'i3 through which air may be added to maintainthe lead sulfide more or Vless in suspension. In carrying out theregeneration, it is sometimes desirable to introduce sour plant gasesthrough line i2 and Yvalve i3 whereby any remaining plumbite in thespent solution isy precipitated as lead sulfide.

Spent caustic solution comprising largely sodium sulfide is then removedthrough line Tand valve lli. The remaining solution `containing leadsulfide is made up to strength by introducingva mixture of fresh andregenerated caustic solution through line 'del and Valve 15, joiningwith line iii. `The lead concentration is made up When necessary 'byadding litharge from slurry pot Ti, entering through linel 't8 and valve'19. A portion of the doctor solution from storage 6? may be passedthrough line 76 and Vlalve 80 to regenerating tower 58. The doctorsolution for use in the plant is passed through'line 8l, valve 32, pump83 and valve 84 and thence by previously described routes to thesweetening plant. A portion ofthe doctor solution as previouslyindicated, passes through line 55 to coagulator 34..

The advantage of the present. process over those usually used lies inthe combination of steps employed whereby improved results are obtained.One of these advantages lies in utilizing the caustic solution to thebest advantage for removing a portion of the mercaptans from thegasoline and using a part of the regenerated caustic to make up thedoctor solution to be used'in the subsequent doctor sweetening step.

By rst mixing they doctor solution and the sour gasoline, followed byadding the sulfur, the

amount 'of elemental sulfur' necessary to completely sweeten thegasoline and to cause ready separation of the lead sulfide may bereduced. By using the coagulator after the initial settling step, it ispossib-le to bring about a greater recovery of chemicals and a cleanerseparation of gasoline than by the usual methods of operation. This isimportant not only from the standpoint of saving chemicals, but alsobecause the sweetened gasoline may be used in blends containing guminhibitors, many of which are soluble in alkaline solutions and removedthereby. A further advantage of the process lies in the method ofreactivating under pressure and of making up fresh doctor solutionduring the regeneration step.

The following example is given tc illustrate the usefulness andpracticability of the process, but should not be construed as limitingit to the exact properties used therein.

A West Texas cracked gasoline, when treated by the usual method ofoperation, had an induction period of minutes which increased with 0.01%of a commercial gum inhibitor to 215 minutes. The copper dish gum, aftertreatment, amounted to ml. per 100 cc. The gasoline contained 0.02% offree sulfur. The octane number was 68.1.. After swcetening according tothe method of the present process, an induction period of 345 minutesand a copper dish gum of 18 ml. per 100 cc. were obtained when using0.01% sulfur content was 0.002% and the octane number was 69.3. Inaddition, approximately 30% less caustic was required than in theprevious mode of operation and the saving of about 30% of lead oxide wasalso observedV when the plant operation was converted'to that of thepresent invention over that o-btained by the conventional method ofoperation.

. We 4claim as our invention:

1. A process for sweetening gasoline which.

comprises contacting said gasoline with an aqueous solution of sodiumhydroxide at a temperature of approximately 50-100 F., separating thespent solution, treating it in the presence of steam to regenerate it,returning a portion of the regenerated sodium hydroxidefor further.

use in the process, supplying another portion of said solution for usein the doctor solution regeneration step as hereinafter described,contacting the gasoline washed with said sodium hydroxide solution withdoctor solution to form lead mercaptides, adding thereto sulfurdissolved in sweetened gasoline to convert said mercaptides to disuldesand lead sulfide, removing a major portion of the spent doctor treatingsolution, contacting the gasoline with. fresh doctor solution,separating the gasoline therefrom, passing the spent doctor treatingsolution to a doctor regeneration plant, treating the spent solutionwith a hydrogen sulfide-containing gas to precipitate the lead suliidedissolved therein, removing the spent alkaline solution, mixing the leadsulfide so precipitated with a portion of the sodium hydroxide solutionfrom the aforesaid respent sodium hydroxide solution, treating it withsteam at a temperature within the range of ap-Y- of the commercialinhibitor. vThe freev proximately 1GO-250 F., to regenerate it,returning a portion of the regenerated solution together with additionalfresh solution to said treating step, separating the gasoline, mixing itwith doctor solution to convert the mercaptans contained therein intolead mercaptides, adding free sulfur dissolved in sweetened gasoline toconvert said mercaptidesY into lead sulde and organic disuldes,separating a major portion of the spent treating solution in a primarysettling step, contacting the treated gasoline with fresh doctorsolution in a secondary step, separating additional spent treatingsolution from said gasoline in a tertiary step, recovering the sweetenedgasoline, passing the spent doctor treating solution to a reactivationstep, contacting it with an oxygen-containing gas at a temperature ofapproximately 170250 F., recovering the regenerated solution andreturning it for further use in the sweetening process.

CHARLES DOAK LOWRY, JR. ROBERT E. SUTHERLAND.

